Amplifying circuit arrangement with parallel supply



May 8, 1934- J. L. H. JONKER El AL 1,957,542

AMPLIFYING CIRCUIT ARRANGEMENT WITH PARALLEL SUPPLY Filed June 22 1931 lNVENTORS JOHAN L. H. JONKER WILHELM ALBRICHT AT-TORNEY Patented May 8, 1934 UNETEE STATES PTENT FFECE AMPLEFYIN G CIRCUIT ARRANGEMENT WITH PARALLEL SUPPLY poration of Delaware Application June 22, 1931, Serial No. 545,946 In the Netherlands June 21, 1939 4 Claims.

(Granted under the provisions of sec. 14, act of March 2, 1927; 357 0. G. 5)

The invention relates to an amplifier circuitarrangement with parallel feeding. With this kind of circuit-arrangements the direct current is commonly supplied to the anode through a choke coil opposing" a very high impedance to all hardly be fulfilled and it has therefore been proposed to connect a saturated diode instead of the choke coil. Beside a comparatively low direct-current resistance such a diode has a very high alternating-current resistance which moreover is independent of the frequency. On superficial consideration the saturated diode seems to be therefore a coupling element having very favourable properties In practice it appears however that the use of a diode does not lead to the desired result and that it is impossible to amplify uniformly a broad range of frequencies.

The invention is based on the view that the unsatisfactory Working of this circuit-arrangement isdue to the fact that with the use of a saturated idiode the filament is connected to a battery or other source of current, owing to which the filament obtains a comparatively large capacity with respect to earth. Since on the other hand the filament of the amplifier valve has also an appreciable capacity relatively to earth, the diode acting as a coupling element is shunted by a rather large capacity. The coupling element consequently has not a very high alternating-current resistance for comparatively high frequencies.

According to the invention, in order to eliminate this drawback use is made of a diode with an indirectly heated cathode.

With a diode comprising an indirectly heated cathode the capacity of the latter relatively to Iearth can be kept very small and need in general not be larger than the capacity between the grid and the cathode of the valve with which the first valve is coupled.

According to the invention, in order to avoid that the capacity of the cathode due to the close proximity of the heating element with the electric circuits connected thereto obtains notwithstanding at considerable value, the heating element may be arranged in such manner that the electrostatic capacity between the cathode and the heating element is very small. For example, the heating coil may be arranged at the exterior around the anode so that the supply of heat to the cathode takes place across the anode. Besides, according to the invention, use is preferably made of a cathode which is very thin. This affords the advantage that the electric field strength perpendicular to the cathode may obtain a high value and this high value of the field strength causes again that the alternating-current resistance of the whole diode is altered.

In fact, the alternating current impedance of the saturated diode which at first seems to be infinitely high, depends in reality on the absolute temperature and on the electric field strength. at the surface of the cathode.

The general character of the expression of the alternating current resistance is thus:

In this expression a denotes a constant, T the absolute temperature and F the field strength perpendicular to the cathode surface. Wh n use is made of a heating coil, surrounding the anode, heating of the latter is of course unavoidable but a heated anode has no harmful effect on the working of the diode, even not if the temperature is so high that the anode begins to emit, for after being emitted the electrons immediately attain an electrostatic field which drives them back to the anode.

The invention is disclosed in the accompanying drawin in which Figs. 1 and 2 represent diagrammatically an approved form of the apparatus and a modification thereof. In Fig. 1 the diode 5 is connected in the direct current ci cuit 6 of the repeater tube 7. The diode comprises a fine wire cathode 8, an anode 9 surrounding the cathode and a heater coil 1G wound around the exterior of the anode. The anode or B battery 11 is connected to the anode 9 of the diode 5. The direct current circuit for the device 7 is from the positive side of the battery 11 to anode 9, cathode 8, through circuit 6 to the anode of device 7 through ground to the negative side of battery 11.

In the modification illustrated in Fig. 2, the cathode 8 is surrounded by a heater element 12 which comprises the anode of the device. Otherwise the circuit of Fig. 2 is the same as the circuit of Fig. 1.

The invention is applicable to high-frequency as well as low-frequency amplifier circuit-arrangements of any kind, quite independently of the purpose for which the apparatus having such a circuit-arrangement are utilized. The invention may also be applied in order to couple the anode circuit of a detector valve with the succeeding lowfrequency amplifier or with a telephone or other indicator.

What we claim is:

1. A repeater circuit comprising a space discharge device having an anode therein, parallel paths connected to said anode, one of said parallel paths comprising a circuit for supplying anode potential to said anode, said circuit including a saturated diode having an indirectly heated cathode.

2. A repeater circuit comprising a space discharge device, an anode in said device, a circuit for supplying direct current to said anode, and a diode in said direct current circuit for providing a high impedance to alternating current and a low impedance to direct current, a small cathode to anode and cathode to ground capacity in said diode whereby the high alternating current impedance of said diode is maintained up to a very high frequency.

3. A repeater circuit including a space discharge device, an anode in said device, a pair of parallel circuits connected to said anode, one of said parallel circuits comprising a direct current circuit, a saturated diode in said direct current circuit, and an indirectly heated cathode in said saturated diode whereby the capacity effectively shunting said diode is minimized and the alternating current impedance of said diode is maintained high over a large range of frequencies.

4. A repeater circuit including a space discharge device, an anode in said device, a direct current circuit for said anode, a saturated diode and a source of anode potential in said direct current circuit, and a small indirectly heated cathode in said diode arranged to have a small capacity with the other element of said diode and the elements of said repeater circuit.

J OHAN LODEWIJK HENDRIK J ONKER. WILHELM ALBRICHT. 

